Method for hydrogenating nitrile functions into amine functions

ABSTRACT

The present invention relates to a process for the hydrogenation of nitrile functional groups to amine functional groups. It relates more particularly to a process for the complete or partial hydrogenation of dinitrile compounds to diamine or aminonitrile compounds.  
     The invention relates to a process for the hydrogenation of nitrile functional groups to amine functional groups using hydrogen in the presence of a hydrogenation catalyst and of a strong inorganic base preferably deriving from an alkali metal or alkaline earth metal. According to the invention, the process comprises a stage of conditioning the catalyst which consists in mixing the hydrogenation catalyst, a predetermined amount of strong inorganic base and a solvent in which the strong inorganic base is not very soluble. This solvent is an amine compound, such as hexamethylenediamine in the case of the hydrogenation of adiponitrile to HMD and/or aminocapronitrile.

[0001] The present invention relates to a process for the hydrogenationof nitrile functional groups to amine functional groups.

[0002] It relates more particularly to a process for the complete orpartial hydrogenation of dinitrile compounds to diamine or aminonitrilecompounds.

[0003] Hydrogenation of dinitriles to the corresponding diamines is aprocess which has been used for a long time, in particular hydrogenationof adiponitrile to hexamethylenediamine, one of the base materials inthe preparation of polyamide-6,6.

[0004] An increasing interest has become apparent in recent years in thehydrogenation (also sometimes known as hemihydrogenation) of aliphaticdinitriles to aminonitriles, in particular the hydrogenation ofadiponitrile to 6-aminocapronitrile, resulting either directly or viacaprolactam in polyamide-6.

[0005] Thus, U.S. Pat. No. 5,151,543 discloses a process for theselective hydrogenation of aliphatic dinitriles to the correspondingaminonitriles, at 25-150° C. and under a pressure of greater thanatmospheric pressure, in the presence of a solvent in a molar excess ofat least 2/1 with respect to the dinitrile, the solvent comprisingliquid ammonia or an alcohol with 1 to 4 carbon atoms and an inorganicbase which is soluble in the said alcohol, in the presence of a Raneycatalyst, the aminonitrile obtained being recovered as main product.

[0006] Patent WO-A-93/16034 discloses a process for the preparation of6-aminocapronitrile by hydrogenation of adiponitrile in the presence ofan inorganic base, of a transition metal complex, the transition metalbeing of low valency and chosen from chromium, tungsten, cobalt andiron, and of Raney nickel as catalyst, under hydrogen pressure and at atemperature of 50° C. to 90° C.

[0007] Patent WO-A-96/18603 discloses the hemihydrogenation of aliphaticdinitriles to aminonitriles by hydrogen in the presence of a catalystbased on optionally doped Raney cobalt or nickel and of a stronginorganic base, the starting hydrogenation medium comprising water,aminonitrile and/or diamine which are capable of being formed andunconverted dinitrile.

[0008] All these hydrogenation processes result in the desiredaminonitrile and are presented as being able to be employed continuouslyin an industrial plant.

[0009] However, the selectivities and the yields of these processes haveto be improved to render them more competitive.

[0010] One of the aims of the present invention is to provide a processfor the hydrogenation of nitrile functional groups in the presence of acatalyst exhibiting an improved yield and an improved selectivity.

[0011] To this end, the invention provides a process for thehydrogenation of nitrile functional groups to amine functional groupsusing hydrogen in the presence of a hydrogenation catalyst and of astrong inorganic base preferably deriving from an alkali metal oralkaline earth metal.

[0012] According to the invention, the process comprises a stage ofconditioning the catalyst which consists in mixing the hydrogenationcatalyst, a predetermined amount of strong inorganic base and a solventin which the strong inorganic base is not very soluble. According to theinvention, the medium comprising a catalyst thus conditioned is fed intothe hydrogenation reactor, the hydrogenation reaction being carried outaccording to the usual conditions or procedures already disclosed in theliterature.

[0013] The term “hydrogenation catalyst” is understood to mean, inparticular and advantageously, Raney metals, such as Raney nickel orRaney cobalt, mixed oxides with a hydrotalcite structure, as disclosedin WO97/10052, but also supported metals, in particular metals fromGroup VIII of the Periodic Table of the Elements, such as nickel,cobalt, ruthenium or rhodium, deposited on a support, which is generallya metal oxide or active charcoal.

[0014] In the case of Raney metals, their instability on contact withthe air requires the use of a liquid storage medium. This liquid mediumis generally water.

[0015] According to the invention, the solvent used exhibits a goodaffinity for the storage liquid, generally water, thus making itpossible to obtain phase separation and formation of a phase comprisingthe strong inorganic base at a high concentration.

[0016] According to a preferred embodiment, the strong inorganic base isadded to the said storage medium before the addition of the solvent.

[0017] In the case of the other catalysts, which do not require thepresence of a storage liquid, it may be worthwhile and advantageous toadd water to the mixture.

[0018] The term “affinity between the solvent and the storage liquid orwater” should be understood as meaning that these compounds are solublein one another.

[0019] Likewise, the term “not very soluble” used to characterize thesolubility of the strong inorganic base in the solvent should beinterpreted as meaning a solubility of less than 3% by weight of thesaid base in the pure solvent.

[0020] According to the invention, the order of addition of thecomponents or the mixture is immaterial.

[0021] According to the process of the invention, the presence of thesolvent results in a phase separation of the strong inorganic base or ofa concentrated solution of strong inorganic base, forming a secondliquid phase comprising all or essentially all of the amount of baseadded to the mixture, this said phase comprising the strong base beingand remaining in intimate contact with the catalyst, the first phasebeing formed by the solvent and the storage liquid and optionally thesolvent of the base, if the latter is added in the form of a solution ina solvent, such as water.

[0022] Therefore, the catalyst particles come into contact with aconcentrated solution of strong inorganic base, allowing the catalyst tobe conditioned by attachment or adsorption of the molecules of strongbase at the surface of the said catalyst.

[0023] The use of a catalyst comprising molecules of strong base at itssurface makes it possible to carry out a hydrogenation with an improvedyield and selectivity which are reflected in particular by a decrease inthe impurities formed, as is illustrated in the examples given below.

[0024] The hydrogenation catalyst can advantageously comprise, inaddition to the catalytic metal, a doping element chosen from theelements from Groups Ib, IIb, IVb, VIb, VIIb and VIII of the PeriodicTable of the Elements, as published in the Handbook of Chemistry andPhysics (Weast, 5th edition of 1970-1971), and aluminium, present inparticular in Raney metals.

[0025] The term “Raney metal” is understood as meaning in particularRaney nickel or Raney cobalt.

[0026] The strong inorganic bases which are suitable for the inventionare alkali metal or alkaline earth metal hydroxides, for example LiOH,NaOH, KOH, RbOH, CsOH, and their mixtures.

[0027] According to another characteristic of the invention, the liquidstorage medium for the Raney metal is preferably water.

[0028] According to one characteristic of the invention, the amount ofstrong base added in the stage of conditioning the catalyst is between0.1 mol and 50 mol per kg of catalyst. The ultimate amount of base isdetermined for each catalyst.

[0029] According to a preferred form of the invention, the strong baseis added in the conditioning stage in the form of a concentratedsolution or in the pure form.

[0030] Furthermore, the amount of solvent added depends on the degree ofsolubility of water or of the storage liquid in this solvent and on thedesired level of concentration in the phase comprising the strong base.Advantageously, the ratio by weight of the solvent to the water (orstorage liquid) will be at least equal to 1, preferably greater than orequal to 2.

[0031] According to the invention, the solvent is chosen from thecompounds which have an affinity (solubilizing ability, for example) forwater or the storage liquid for the Raney metal and which, in contrast,do not have an affinity (low solubilizing ability) for the stronginorganic base. The concept of insolubility of the strong base in thesolvent or more specifically in the liquid phase formed by the solventand the water or the storage liquid should be understood as meaning alow solubility of the base, for example of less than 1% by weight.

[0032] In a preferred embodiment of the invention, the solvent isadvantageously an amine, preferably an amine corresponding to thatobtained by the hydrogenation reaction, or liquid ammonia, in the casewhere the hydrogenation is carried out in a liquid ammonia medium. Thisis because the choice of the solvent should advantageously not allow newsubstances to be introduced into the hydrogenation medium and thusshould make possible easy and inexpensive separation and optionallyrecycling processes which are thus not very penalizing for the processfrom a technical and economical viewpoint.

[0033] The stage of conditioning the catalyst can be carried out underan inert atmosphere, optionally under a hydrogen atmosphere or underhydrogen pressure.

[0034] The process of the invention applies more particularly to thehydrogenation of dinitriles, such as adiponitrile, to diamines, such ashexamethylenediamine (HMD), or to the partial hydrogenation orhemihydrogenation of dinitriles, such as adiponitrile, to aminonitriles,such as aminocapronitrile. The latter reaction is particularlyadvantageous for the manufacture of lactams, such as ε-caprolactam,obtained by cyclizing hydrolysis of the aminonitrile.

[0035] Generally, this hemihydrogenation reaction is carried out in thepresence of water, which represents between 0.1 and 20% by weight of thereaction medium, or in the presence of another compound, for exampleliquid ammonia, the concentration of this compound advantageously beingless than 50% by weight of the reaction medium.

[0036] Thus, in a specific embodiment of a hemihydrogenation, thestarting hydrogenation medium comprises water in a proportion of atleast 0.5% by weight with respect to all the liquid compounds of thereaction medium. The medium also comprises one or more diamines and/oraminonitriles, capable of being formed from the dinitrile byhydrogenation with hydrogen, and unconverted dinitrile in a proportion,for the combination of these three compounds, of 80% and 99.5% by weightwith respect to the combined liquid compounds of the reaction medium.

[0037] The aliphatic dinitriles which can be employed in the process ofthe invention are more particularly the dinitriles of general formula(I):

NC—R—CN  (I)

[0038] in which R represents a linear or branched alkylene or alkenylenegroup having from 1 to 12 carbon atoms.

[0039] Use is preferably made, in the process of the invention, ofdinitriles of formula (I) in which R represents a linear or branchedalkylene radical having from 2 to 6 carbon atoms.

[0040] Mention may in particular be made, as examples of suchdinitriles, of adiponitrile, methylglutaronitrile, ethylsuccinonitrile,malononitrile, succinonitrile, glutaronitrile and their mixtures, inparticular the mixtures of adiponitrile and/or of methylglutaronitrileand/or of ethylsuccinonitrile which can originate from the same processfor the synthesis of adiponitrile.

[0041] In practice, the case where R=(CH₂)₄ will be the most frequent asthis corresponds to the use of adiponitrile (ADN) in the presentprocess.

[0042] It is also possible, in the process of the invention, to add astrong base to the hydrogenation reaction medium which is identical toor different from that used for the conditioning of the catalyst. Thisstrong base is generally an alkali metal or alkaline earth metalhydroxide, carbonate or alkoxide.

[0043] The reaction medium has a composition varying according to thetype of implementation of the process.

[0044] This is because, if the process is carried out batchwise, as isin particular the case in tests on the laboratory scale or forsmall-scale manufacturing trials, the starting reaction medium willgradually grow richer in aminonitrile and, to a lesser extent, indiamine, whereas the concentration of dinitrile can either decrease, ifall or most of the said dinitrile is charged from the beginning of thehemihydrogenation, or can remain relatively constant, if the dinitrileis introduced gradually during the reaction.

[0045] In contrast, if the process is carried out continuously, theaverage composition of the reaction medium reaches values predeterminedby the degree of conversion and the selectivities of the reaction.

[0046] Water is usually present in an amount of less than or equal to20%. The water content of the reaction medium is preferably between 0.5%and 15% by weight with respect to the combined liquid constituents ofthe said medium.

[0047] The concentration of the targeted aminonitrile and/or of thecorresponding diamine and of the unconverted dinitrile in the reactionmedium is generally between 85% and 98% by weight with respect to thecombined liquids included in the said reaction medium.

[0048] The catalysts used in this hemihydrogenation process can be aRaney nickel or a Raney cobalt comprising, in addition to the nickel orthe cobalt and the residual amounts of the metal removed from thestarting alloy during the preparation of the catalyst, that is to saygenerally aluminium, one or more other elements, often known as dopingelements, such as, for example, chromium, titanium, molybdenum, copper,tungsten, iron or zinc. Among these doping elements, chromium, copper,titanium, iron and their mixtures are regarded as the most advantageous.These doping elements usually represent, by weight with respect to theweight of nickel or of cobalt, from 0% to 15% and preferably from 0% to10%.

[0049] Use may also advantageously be made of a catalyst based onruthenium deposited on a support composed of acetylene black. Thiscatalyst can also comprise doping metal elements included in the listmentioned for the Raney metals.

[0050] The amount of catalyst employed can vary very widely according inparticular to the nature of the catalyst and the method of operationadopted or the reaction conditions chosen. By way of indication, use maybe made of 0.5% to 50% by weight of catalyst, expressed as weight ofmetal with respect to the total weight of the reaction medium, andgenerally of 1% to 35% by weight.

[0051] The process of the invention is generally carried out at areaction temperature of less than or equal to 150° C., preferably ofless than or equal to 120° C. and more preferably still of less than orequal to 100° C.

[0052] In concrete terms, this temperature is between ambienttemperature (approximately 20° C.) and 100° C.

[0053] Prior to, simultaneously with or subsequent to the heating, thereaction chamber is brought to the appropriate hydrogen pressure, thatis to say, in practice, between 1 bar (0.10 MPa) and 100 bar (10 MPa)and preferably between 5 bar (0.5 MPa) and 50 bar (5 MPa).

[0054] The other conditions which govern the hydrogenation (continuousor batchwise) in accordance with the invention relate to conventionaltechnical arrangements which are known per se.

[0055] Furthermore, these conditions can be modified in order to modifythe degree of conversion of the dinitrile to diamine according towhether a high selectivity for aminonitrile is desired or converselycomplete hydrogenation of the dinitriles to diamines is desired.

[0056] The following examples, given solely by way of indication,illustrate the invention.

[0057] In these examples, the following abbreviations may be used:

[0058] ADN=adiponitrile

[0059] ACN=aminocapronitrile

[0060] HMD=hexamethylenediamine

[0061] DC=degree of conversion (% by weight of adiponitrile converted)

[0062] YD=selectivity with respect to the converted starting substrate(mol % of compound ACN (YD_(ACN)) or HMD (YD_(HMD)) obtained withrespect to the total amount of ADN converted).

EXAMPLE 1

[0063] 0.806 g of potassium hydroxide, in solution in 4.2 g of water, ismixed with 37.8 g of hexamethylenediamine in a stirred reactor.

[0064] The mixture is kept stirred at 80° C. A two-phase system isformed. The organic phase, comprising the HMD, is analysed to determinethe water content and potassium hydroxide content. The results are asfollows:

[0065] Water content: 8.2% by weight

[0066] Potassium hydroxide concentration: 0.0287% by weight

[0067] The aqueous phase is thus an approximately 50% by weightpotassium hydroxide solution.

[0068] The amount of potassium hydroxide present in the organic phaserepresents 1.5% of the amount of potassium hydroxide charged.

EXAMPLES 2 AND 3

[0069] Example 1 is repeated by mixing 252 g of HMD, 126 g of ethanoland 5.76 g of sodium hydroxide in solution in 42 g of water.

[0070] Analysis of the organic phase obtained after stirring shows thatit comprises 7.16% by weight of water and 0.3252% of sodium hydroxide.

[0071] This result shows that approximately 25% of the sodium hydroxidecharged is found in the organic phase, which comprises a solvent of thesodium hydroxide, namely ethanol.

[0072] Similar tests, without ethanol but using 378 g of HMD instead of252 g, makes it possible to obtain a concentration of sodium hydroxidein the organic phase of 0.0496%. In this example, 3.6% of the sodiumhydroxide charged is found in the organic phase.

EXAMPLE 4

[0073] Analogously to Example 1, 20 g of Raney nickel, present in 18 gof water, are mixed with 180.9 g of hexamethylenediamine and 0.896 g ofpotassium hydroxide in solution in 4.23 g of water. The mixture isstirred at 80° C.

[0074] Analysis of the HMD-based organic phase shows that it comprises10.2% by weight of water and 0.0123% by weight of potassium hydroxide.The amount of potassium hydroxide present in the organic phaserepresents 2.8% of the potassium hydroxide charged. 97.2% by weight ofthe potassium hydroxide charged is thus in direct contact with thecatalyst.

EXAMPLE 5

[0075] 240 g of HMD, 52 g of water and 6.4 g of Raney nickel doped with1.5% by weight of chromium are charged to a stirred reactor. 0.462 ml ofa 388 g/l potassium hydroxide solution are added in order to obtain aKOH/Ni ratio of 0.5 mol/kg. The mixture is kept stirred at a temperatureof 50° C. The reactor is placed under hydrogen pressure at 25 bar.

[0076] 40 g of adiponitrile are added to the reactor. After reacting for50 minutes, the medium is cooled and analysed by gas chromatography todetermine the total degree of conversion (DC) of the adiponitrile (ADN),the selectivity (YD_(ACN)) of the reaction for aminocapronitrile (ACN)and the Poln concentration of the medium.

[0077] This polarographic number represents in particular theconcentration of imine compounds in the medium. It is determined bypolarography and is expressed in moles of imine functional group pertonne of sample to be quantitiatively determined.

[0078] Degree of conversion of ADN (DC): 83.8%

[0079] Selectivity for ACN (YDACN): 68.3%

[0080] Poln in mol/t: 21

COMPARATIVE EXAMPLE 6

[0081] Example 5 was repeated but with addition of the potassiumhydroxide simultaneously with the adiponitrile. The amounts added areidentical.

[0082] The results obtained are as follows:

[0083] Degree of conversion of ADN (DC): 81.1%

[0084] Selectivity for ACN (YD_(ACN)): 69.7%

[0085] Poln in mol/t: 76

[0086] This results clearly shows the effect of the stage ofconditioning the catalyst on the purity of the product obtained.

EXAMPLE 7 AND COMPARATIVE EXAMPLE 8

[0087] A catalyst based on ruthenium doped with 1% by weight of iron onan acetylene black support, sold under the name Y 70, is obtained by thefollowing process:

[0088] 20 g of Y70 acetylene black, sold by SN2A, are charged to 800 mlof water. The suspension is heated to 90° C. with stirring. 1.8 g ofNa₂CO₃ in a total of 70 ml of water are added. After a period of 1 hour,a solution of 2.16 g of RuCl₃ hydrate in 120 ml of water is added. After1 hour, a solution of 1 g of FeCl₃ hexahydrate in a total of 70 ml ofwater is run in. After a further hour, the medium is allowed to cool toa temperature of 40° C.

[0089] After filtration, the catalyst is washed with 4 times 200 ml ofwater at 40° C.

[0090] The catalyst is dried in an oven for 1 hour at 120° C. 21.3 g ofcatalyst are obtained.

[0091] Before the test, it is dried in an oven for 10 hours at 80° C.under reduced pressure. 2.4 g of catalyst prepared according to theabove process, 4.8 g of water and 5 g of 15N potassium hydroxide areadded to 36 g of HMD.

[0092] The medium is mixed at a temperature of 80° C. and placed under ahydrogen pressure of 2.5 MPa. 36 g of adiponitrile are added to thismedium.

[0093] After reaction, the medium is analysed.

[0094] The following results are obtained:

[0095] reaction time: 105 min

[0096] DC of the ADN: 67%

[0097] YD_(ACN) 75%

[0098] Poln 35 mol/t

[0099] A test using the procedure of Comparative Example 6 and themasses and products used in the above Example 7, in particular the samecatalyst, gave the following results:

[0100] reaction time: 110 min

[0101] DC of the ADN: 68.5%

[0102] YD_(ACN) 73%

[0103] Poln 92 mol/t

1. Process for the hydrogenation of nitrile functional groups to aminefunctional groups using hydrogen in the presence of a hydrogenationcatalyst and of a strong inorganic base deriving from an alkali metal oralkaline earth metal, characterized in that it comprises a stage ofconditioning the catalyst which consists in mixing the catalyst, apredetermined amount of strong inorganic base to be associated with thecatalyst and a solvent in which the strong inorganic base is not verysoluble, the said mixture comprising the conditioned catalyst being fedinto the hydrogenation reaction medium comprising the compound to behydrogenated and optionally a solvent.
 2. Process according to claim 1,characterized in that the hydrogenation catalyst is chosen from thegroup consisting of Raney metals, metals from Group VIII of the PeriodicTable of the Elements deposited on a support, and mixed oxides with ahydrotalcite structure.
 3. Process according to claim 2, characterizedin that the Raney metal is Raney nickel or Raney cobalt.
 4. Processaccording to claim 2, characterized in that the metals from Group VIIIare chosen from the group consisting of nickel, cobalt, ruthenium andrhodium, the support being chosen from metal oxides, active charcoal oracetylene blacks.
 5. Process according to one of the preceding claims,characterized in that, when a liquid known as a storage liquid isassociated with the use of the catalyst, in particular a catalyst basedon Raney metal, the abovementioned solvent and the said storage liquidare soluble in one another, the strong inorganic base not being verysoluble in the solution of the solvent and of the storage liquid. 6.Process according to one of the preceding claims, characterized in thatthe mixture for conditioning the catalyst comprises water.
 7. Processaccording to claim 5 or 6, characterized in that water is a liquid forstorage of the hydrogenation catalyst.
 8. Process according to one ofthe preceding claims, characterized in that the solvent is a compoundcomprising one or more amine functional groups or liquid ammonia. 9.Process according to claim 8, characterized in that the solvent is anamine compound formed by the hydrogenation reaction or is identical to acompound formed by the hydrogenation reaction.
 10. Process according toone of the preceding claims, characterized in that the strong inorganicbase is added to the liquid medium for storage of the Raney metal beforethe addition of the solvent.
 11. Process according to one of thepreceding claims, characterized in that the stage of conditioning thecatalyst is carried out under an inert atmosphere.
 12. Process accordingto one of claims 1 to 10, characterized in that the stage ofconditioning the catalyst is carried out under a hydrogen atmosphere orhydrogen pressure.
 13. Process according to one of the preceding claims,characterized in that it consists in hydrogenating a dinitrile to anaminonitrile and/or to a diamine.
 14. Process according to claim 13,characterized in that the dinitrile is adiponitrile and in that itconsists in hydrogenating adiponitrile to aminocapronitrile and/orhexamethylenediamine.
 15. Process according to either of claims 13 and14, characterized in that the solvent is hexamethylenediamine. 16.Process according to one of the preceding claims, characterized in thatthe ratio by mass of the solvent to the liquid medium for storage of thecatalyst or the water in the mixture for conditioning the catalyst is atleast equal to
 1. 17. Process according to one of the preceding claims,characterized in that the concentration of catalyst in the conditioningmixture is less than or equal to 30% by weight, expressed as weight ofmetal.
 18. Process according to one of the preceding claims,characterized in that the catalyst comprises doping elements. 19.Process according to claim 18, characterized in that the Raney metal isRaney nickel, the doping element or elements being chosen from theelements from Groups Ib, IIb, IVb, VIIb and VIII of the Periodic Tableof the Elements.
 20. Process according to claim 18, characterized inthat the Raney metal is Raney cobalt, the doping element or elementsbeing chosen from the group consisting of the elements from Groups Ib,IIb, IVb, VIb, VIIb and VIII of the Periodic Table of the Elements.